import javax.swing.text.AbstractDocument.LeafElement;

/**
 * Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.
 * 
 * For example,
 * 123 -> "One Hundred Twenty Three"
 * 12345 -> "Twelve Thousand Three Hundred Forty Five"
 * 1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"
 */
public class _273IntegertoEnglishWords {
    private static final String[] LESS_THAN_20 = { "", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight",
            "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen",
            "Nineteen" };
    private static final String[] TENS = { "", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy",
            "Eighty", "Ninety" };
    private static final String[] THOUSANDS = { "", "Thousand", "Million", "Billion" };

    public String numberToWords(int num) {
        if (num == 0) {
            return "Zero";
        }
        int i = 0;
        String result = "";
        while (num > 0) {
            if (num % 1000 != 0) {
                result = helper(num % 1000) + THOUSANDS[i] + " " + result;
            }
            num /= 1000;
            i++;
        }
        return result.trim();
    }

    private String helper(int num) {
        if (num == 0) {
            return "";
        } else if (num < 20) {
            return LESS_THAN_20[num] + " ";
        } else if (num < 100) {
            return TENS[num / 10] + " " + helper(num % 10);
        } else {
            return LESS_THAN_20[num / 100] + " Hundred " + helper(num % 100);
        }
    }
}